Using propane to diagnose a carb problem... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Cal69Chevy · 04-01-2002, 12:36 PM

As some of you are aware I've been having a problem with the engine sputtering off idle. I was talking with a man that rebuilds carbs and he gave me this 'tip'.

He suggests that I reproduce the sputtering by putting the truck in drive with both the emergency and operating brake on and accelerate to the point where the sputtering starts. This is where it gets interesting. He suggests having a hand held propane torch available and positioned so propane can be released into the carb. just as the stumble starts open the propane valve releasing propane into the carb. If the stumble goes away then it is a fuel starvation carb problem....if not it is likely a vacuum adv. problem.

Sounds like it might work. Have any of you ever tried this? The truck has never backfired so I feel reasonably safe from being blown up...however it's never run on propane before either!

68 Suburban · 04-01-2002, 01:34 PM

Just make sure you are not standing in front of the truck! lol

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Cal69Chevy · 04-01-2002, 06:24 PM

TTT

Eddie H. · 04-01-2002, 07:53 PM

Back in the "OLD DAYS" before electronic fuel injection, us old time mechanics used propane as a diagnostic tool. It can be very useful for finding vacuum leaks, carb problems, lean missfire, etc.
I suggest that you be safe and put a length of rubber vacuum hose on the end of your torch and run it into the air cleaner, Then while setting in the truck and loading it up in gear until it acts up, slowly open the valve and see if it smooths out. If so, you have a lean missfire.

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raychevy · 04-01-2002, 08:06 PM

I wouldnt be standing in front of a revin truck.

Cal69Chevy · 04-01-2002, 09:20 PM

Eddie..thanks for the hose idea...sounds much safer that way...

bigjimzlll · 04-01-2002, 09:46 PM

In the old days we would do a "propane inrichment test"....To find a manifold vacuum leak, we would put propane in the crank case...if the idle smoothed out, it was a manifold, or other internial problem...remember this was the old days and we did do alot of things I wouldnt do now...lol

[This message has been edited by bigjimzlll (edited April 01, 2002).]

04-01-2002, 12:36 PM	#1
Cal69Chevy Registered User Join Date: Nov 2001 Location: SoCal Posts: 136	Using propane to diagnose a carb problem... As some of you are aware I've been having a problem with the engine sputtering off idle. I was talking with a man that rebuilds carbs and he gave me this 'tip'. He suggests that I reproduce the sputtering by putting the truck in drive with both the emergency and operating brake on and accelerate to the point where the sputtering starts. This is where it gets interesting. He suggests having a hand held propane torch available and positioned so propane can be released into the carb. just as the stumble starts open the propane valve releasing propane into the carb. If the stumble goes away then it is a fuel starvation carb problem....if not it is likely a vacuum adv. problem. Sounds like it might work. Have any of you ever tried this? The truck has never backfired so I feel reasonably safe from being blown up...however it's never run on propane before either! __________________ '69 Chevy, 4X4-SB 350 TBI-TH350 Trans-205 Transfer Case-Dana 44 Front-14 Bolt Rear-Front Disc Brakes-Factory A/C-P/S Ken's '69 Page

04-01-2002, 01:34 PM	#2
68 Suburban Registered User Join Date: Oct 2000 Location: From Chicago, Live in Phoenix, AZ Posts: 6,802	Just make sure you are not standing in front of the truck! lol ------------------ Check out other members trucks 1968 50th Anniversary C-10 Suburban (Tows all these cars all over the place) 1968 50th Anniversary C-10 Pickup 1968 50th Anniversary C-20 Pickup CST 1969 SS Camaro Conv't 2000 Chevy Malibu (Suppose to be daily driver, but the Burb is) Phoenix, AZ. Click Here for Parts and Venicles I have Available THINGS I AM LOOKING FOR: 67-68 SUBURBAN TRIM. $$$$ Reward for finding the 3rd door trim piece and the small piece that goes on the 1/4 panel right behind the 3rd door. __________________ Just sitting here contemplating contemplation.

04-01-2002, 06:24 PM	#3
Cal69Chevy Registered User Join Date: Nov 2001 Location: SoCal Posts: 136	TTT __________________ '69 Chevy, 4X4-SB 350 TBI-TH350 Trans-205 Transfer Case-Dana 44 Front-14 Bolt Rear-Front Disc Brakes-Factory A/C-P/S Ken's '69 Page

04-01-2002, 07:53 PM	#4
Eddie H. Registered User Join Date: Mar 2001 Location: Paradise TX USA Posts: 1,200	Back in the "OLD DAYS" before electronic fuel injection, us old time mechanics used propane as a diagnostic tool. It can be very useful for finding vacuum leaks, carb problems, lean missfire, etc. I suggest that you be safe and put a length of rubber vacuum hose on the end of your torch and run it into the air cleaner, Then while setting in the truck and loading it up in gear until it acts up, slowly open the valve and see if it smooths out. If so, you have a lean missfire. ------------------ 69 GMC LWB 404/400 daily driver 71 GMC LWB 350/700R4 frame-up restoration in progress __________________ "Negative people always seem to have a problem for every solution"

04-01-2002, 09:20 PM	#6
Cal69Chevy Registered User Join Date: Nov 2001 Location: SoCal Posts: 136	Eddie..thanks for the hose idea...sounds much safer that way... __________________ '69 Chevy, 4X4-SB 350 TBI-TH350 Trans-205 Transfer Case-Dana 44 Front-14 Bolt Rear-Front Disc Brakes-Factory A/C-P/S Ken's '69 Page

04-01-2002, 08:06 PM	#5
raychevy Registered User Join Date: Jul 2000 Location: Evansville, Indiana USA Posts: 485	I wouldnt be standing in front of a revin truck.

04-01-2002, 09:46 PM	#7
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	In the old days we would do a "propane inrichment test"....To find a manifold vacuum leak, we would put propane in the crank case...if the idle smoothed out, it was a manifold, or other internial problem...remember this was the old days and we did do alot of things I wouldnt do now...lol [This message has been edited by bigjimzlll (edited April 01, 2002).] __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA



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